The present invention relates to a process for recovering form an aqueous polymerization solution a relatively high molecular weight polymeric sulfonate, such as polyvinyl sulfonate, which is substantially free of undesirable by-products of sulfonation, and more particularly, to such a process wherein the molecular weight of the polymeric sulfonate, such as polyvinyl sulfonate, which is recovered is increased.
Polymeric sulfonates are conventionally polymerized form commercially available solutions containing a monomer in the presence of a suitable catalyst. For example, polyvinyl sulfonate can be polymerized from a commercially available, dilute, e.g. 25-50 weight percent, aqueous solution of vinylsulfonic acid, sodium salt, in the presence of a suitable catalyst, such as ammonium persulfate or sodium bisulfite. The resultant aqueous polymerization solution contains undesirable by-products of sulfonation, such as sulfate ions and hydroxyethyl sulfonate, and unreacted vinylsulfonic acid, sodium salt monomer, in addition to polyvinyl sulfonate. The presence of such undesirable by-products can be extremely deleterious when polyvinyl sulfonate is used as a scale inhibitor. Addition of large quantities of methanol to an aqueous polymerization solution has been advanced to separate polymeric sulfonates, such as polyvinyl sulfonate, therefrom. However, large quantities of methanol will precipitate polymeric sulfonates and unwanted by-products of sulfonation from the solution. Thus, a need exists for a process for separating polymeric sulfonates, such as polyvinyl sulfonate, from an aqueous polymerization solution also containing unwanted by-products of sulfonation.
Accordingly, it is an object of the present invention to provide a process for recovering and purifying a relatively high molecular weight polymeric sulfonate, such as a polyvinyl sulfonate, by selectively separating unwanted by-products of sulfonation, such as sulfate ions and hydroxyethyl sulfonate, from aqueous solutions containing the polymeric sulfonate.
It is a further object of the present invention to provide a process for enhancing the molecular weight of a relatively high molecular weight polymeric sulfonate, such as a polyvinyl sulfonate.